1. Field of the Invention
The present invention relates to a motor and a driving device for a recording disk, and more particularly, to a motor, which is capable of preventing the overflow of oil within a fluid dynamic bearing while maintaining a pull-out force between a shaft and a hub of a rotor, and a driving device for a recording disk.
2. Description of the Related Art
A small spindle motor used in a driving device for a recording disk is a mechanism that employs a fluid dynamic bearing assembly having a shaft supported by fluid pressure generated by oil interposed between the shaft and a sleeve thereof.
The recent improvement in the performance of driving devices for recording disks has increased the demand for low current, low non-repeatable runout (NNRO), impact resistance, vibration resistance or the like.
In addition, research into oil sealing is actively ongoing in order to prevent oil from flowing over a fluid dynamic bearing assembly when a shaft rotates at a high speed.
Meanwhile, in the fluid dynamic bearing assembly, a shaft hole inside a sleeve into which the shaft is inserted has a tapered upper or lower end to thereby achieve the taper sealing of oil.
However, such taper sealing shortens the bearing span of the shaft, which makes it difficult for the shaft to stably support a rotor.
Of late, a sintered sleeve, capable of containing a large amount of oil, has been used. This causes a significant variation in an oil interface due to the thermal expansion of oil. To prevent an oil overflow, the tapered portion may be elongated. However, this makes it more difficult to support the rotor.